Vertical radiator antenna structure which eliminates the necessity of a ground plane

ABSTRACT

A HIGH FREQUENCY ANTENNA WHICH COMPRISES A TWO SECTION VERTICAL RADIATOR. (CUT TO THE MEDIAM FREQUENCY) APPROXIMATELY FIVE-EIGHTS WAVELENGTH LONG AT ITS HIGHEST OPERATING FREQUENCY. ONE-HALF WAVELENGTH AT ITS LOWEST OPERATING FREQUENCY, WHICH IS END-FED BY A COAXIAL FEED THROUGH THE BASE OF THE RADIATOR. THE POWER SUPPLIED TO THE COAXIAL FEED IS FED SO AS TO BE RESONANT TO THE UPPER AND LOWER FREQUENCY LIMITS OF THE RADIATOR THEREBY SHIFTING THE CURRENT LOBE AWAY FROM THE BASE, IN EFFECT MAINTAINING NEAR ZERO CURRENT AT THE BASE OF THE RADIATOR. THIS PRODUCES A RADIATOR WHICH IS NOT DEPENDENT UPON A GROUND PLANE AND WHICH PATTERN WHILE VERTICALLY POLARIZED IS HORIZONTAL AND OMINIDIRECTIONAL. IN EFFECT,   THE ANTENNA ACTS AS A DUPOLE AT LOWEST FREQUENCY AND A DISPLACED ONE-FOURTH WAVE SECTION AT HIGHEST FREQUENCY.

United States Patent [72] Inventor William Hampton 3,259,901 7/1966 Bykerk .Q 343/7l5X Akron, Ohio 3,267,476 8/1966 Finke 343/715 [2!] Appl. No. 718,522 2,112,287 3/1938 Hansell et a1. 343/791 [22] Filed Apr. 3,1968 2,700,112 1/1955 Jasik 343/792 [45] Patented June 28. 1971 3,438,042 4/1969 Kuecken 343/792 [73] Asslgnee g Corporauon Primary Examiner-Herman Karl Saalbach m Assistant Examiner-Paul L. Gensler Attorney-1.6.Pere [54] VERTICAL RADIATOR ANTENNA STRUCTURE WHICH ELIMINATES THE NECESSITY OF A GROUND PLANE ClaimsSDnwing gs. ABSTRACT: A high frequency antenna which comprises a two section vertical radiator, (cut to the median frequency) U-s.

approximately five eig hths wavelength long at 343/830, 343/873, 343/887, 343/749, 343/848 operating frequency, onehalf wavelength at its lowestoperat- [5 ing frequency is end fed a coaxial feed through the [50] Field of Search 343/715, base f the radiator The power supplied to the coaxia] f d is 705,722, 745, 749, 750, 825, 843, 872, 859, 792, fed so as to be resonant to the upper and lower frequency 887 limits of the radiator thereby shifting the current lobe away 56 R f ed from the base, in effect maintaining near zero current at the I l e It base of the radiator. This produces a radiator which is not de- UNITED STATES PATENTS pendent upon a ground plane and which pattern while verti 2,624,844 1/1953 Nelson et al. 343/790X cally polarized is horizontal and omnidirectional. In effect, the 2,642,529 6/1953 Frankel 343/745X antenna acts as a dipole at lowest frequency and a displaced 3,098,231 7/1963 St. Vrain et al. 343/745 one-fourth wave section at highest frequency.

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|5 /22 SERIESIPARALLEL RESONANT CIRCUITS 24 INVENTOR RE POWER-AND W/LL/A/l/l HAMPTON ANTENNA DRIVE AND RECEWER 65M; 4 04% ATTORNEYS PATENIEDJUN28|97| SHEET 2 BF 2 FIG.-3

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ATTORNEYS I I 1 I 1 r I I VERTICAL MAMATOM ANTENNA S'lllltUC'lllUlkE WllllllCkll ELlMlllhlla l I Til-11d lWEiCEdfillTl! Oil" A GROUND lPlLANlE It is well known that omnidirectional vertical radiator-type antennas are old and have been used in the art for many years. However, these antennas necessarily require a ground plane acting as a support or a base for the antenna, which may be the skin of an aircraft if tle antenna is mounted on an aircraft, automotive vehicle. or the actual ground if the antenna is mounted on the ground. The ground plane tends to reflect and provide interference, ith the electromagnetic radiation from the antenna. Furthei'. where it in desirable for the antenna to be very short, say one-hall" wavelength or less for high frequency electromagnetic radiation, the ground plane provides the undesirable effect of l miting the range of the omnidirectional pattern, as well as forcing the pattern away from the ground plane when a verticallradiator is used, making its use on aircraft moving at high speed unreliable and generally unsatisfactory. 1

Hence, it is the general object of the invention to avoid and overcome the foregoing and other difficulties of and objections to prior art practices by the provisions of a high frequency vertically radiating antenna which has great strength, and hence is usable on high speed vehicles, but which utilizes electrical techniques to drive the antenna so as to eliminate the ground plane, thereby operating independently of a ground plane, and even when the antenna is mounted flush to a metallic surface, the pattern will not be distorted.

An object of the present invention is to provide a simplified, high-strength vertical radiator-typc antenna for use on high speed aircraft. l

The aforesaid objects of the invention and other objects which will become apparent are achieved by providing in an antenna system the combination of a mounting base, a vertical radiator mounted to the base, which radiator comprises a bottom section connected to the base, and a top section connected in insulated cnd-to-end relation to the bottom section, a coaxial feed from the mounting base through the bottom section to end feed the radiator, means to provide current to the coaxial feed, where the antenna system is approximately one-half wavelength long at its lowest operating frequency, and five-eights wavelength at its highest operating frequency, and where a standing wave is produced on the top section upon energization, and which system antenna operates at a near zero current at its base so as to eliminate the necessity of a ground plane.

For a better understanding of the invention reference should be had to the accompanying drawings wherein:

FIG. 1 is an enlarged cross-sectional partially broken away illustration of the antenna of the invention and its preferred embodiment and structure;

FIG. 2 is a graphic illustration of the antenna showing the current lobe on the antenna during operation with current supplied thereto;

FIG. 3 is a schematic illustration of the electromagnetic radiating lobes from an aircraft utilizing the antenna of the invention;

FIG. Al is a modified embodiment of the invention utilizing chokes to achieve the electrical characteristics of the power and antenna drive box of P10. 1; and

FIG. is a cross-sectional illustration of the antenna of FIG. 4 taken on line 5-5 thereof.

The simplest arrangement to consider as a source of radiating electromagnetic energy is a straight conductor center fed, very short compared with the wave length produced and carrying a uniform alternating current. This type of radiator or antenna can be called a dipole. It will be evident from the shape of the dipole, that if it is vertically positioned, its radia tion will be the same in all directions in a horizontal plane, and this radiation can in the normal rad theoretically perfect circumstance look like a doughnut with the dipole aligned with the axis through the hole in the center of the doughnut. The field strength is dependent upon the first power of the distance from the dipole.

Although electromagnetic waves are produced whenever a varying current flows along a conductor, and certain shortwave aerial systems operate by virtue of a traveling wave along a correctly terminated wire, radiation is usually associated with a system in which stationary waves are present, and this invention contemplates the operation of the antenna working under such conditions. In order to radiate at all efficiently, it is necessary that the dimensions of the circuit should be comparable with the wave length of the alternating current introduced, and the simplest method of getting a large current into such a circuit to achieve larger distances of electromagnetic radiation is to produce stationary waves.

With a vertically positioned radiator, the maximum power output is obtained when the current is maximum at the base of the radiator, as this obtains a resonance match between the impedance of the base. Heretoforc in the prior art, it has been the practice to have zero reactancc at the base of a vertical radiator so as to have current maximum at the base. in other words, the sum of the reactances of the radiator and the base should cancel so that current can be maximum at the base. However, this type of vertical radiator does require a ground plane to obtain the desired horizontal radiation from the vertical radiator.

ln contradistinction to this prior art, the invention in essence operates with the current at the base of the antenna system or mounting surface approximately zero with the maximum current occurring at the base of the driven element so that the necessity of the ground plane is eliminated. Operating in this manner high enough energy levels can be achieved to provide long range, and more uniform electromagnetic patterns with relation to the mounting surface.

Thus, with reference to the form of the invention illustrated in FIG. 1 of the drawings, the numeral 10 indicates generally a radiator which is mounted to a base l2 and has a coaxial connector lid. The connector 14 mounts through the skin 13 of an aircraft, for example. The radiator essentially comprises a lower section indicated generally by numeral 16, and an upper section 13. The sections 16 and 18 are held in fixed streamlined relationship to each other by an insulated fiberglass connector 20. The lower section 16 houses a coaxial cable 22 from a power and antenna drive indicated by box 24. The coaxial cable 22 is mounted in insulated relationship with a conductive outer shell 26 by an appropriate insulating layer 28. The outer shell 26 acts as a choke by having its top 260 and its bottom 26!: electrically connected to the coax shielding. The upper section 18 is electrically connected to the coaxial cable 22 by an appropriate wire 30. The sections 16 and 18 are substantially equal in length, and the feed from the coaxial cable utilizes section 18 end fed as a transmitter and receiver element. The section 16 is simply a support for section 18 so that the current approaches zero at the skin 13. This occurs when the antenna is combined with appropriate networks of series-parallel circuits 1S resonant at the upper and lower frequency which effectively shift the current node on section 18 away from the base. Such circuits 15 are well within the skill of one in the art. The invention contemplates that the sections 16 and 18 will be made from a hard-drawn commercial brass with an allowable ultimate tensile strength of 67,000 p.s.i. and an allowable yield strength of 45,000 p.s.i. Preferably, the connector 20 will be made from fiberglass.

The antenna is specifically designed for high efficiency at spaced frequencies, and it provides a vertically polarized wave formed into a horizontal omnidirectional beam. Specifically, operating at UHF conditions the antennas lower frequency is 225 MHz and the upper frequency is 400 MHz.

FIG. 2 illustrates the current loading of the antenna 10 utilized to accomplish the zero current at the base. Specifically, for higher frequencies when section 18 is driven its current loading appears as curve 40 in FIG. 2 which approaches zero near the base, and starts back out again towards the bottom of the upper section 18. For lower frequencies, the loading thereof resembles the curve 42 representing the current which approaches exactly zero at the base of section 16. The

nominal input impedance is 50 ohms at either higher or lower frequency. and the invention requires that a voltage standing wave ratio of between about 1.0 and 2.0, and preferably about L is necessary to meet the objects of the invention.

FIG. 3 represents the type of electromagnetic lobes generated utilizing the antenna of the invention either on the high frequency or low frequency operation, which indicated that one-halfpower is achieved at 11 5 to l5 down angle even from a vertically upward directed antenna 50 mounted on an aircraft 52 because no ground plane is necessary with the antenna of the invention. It has been found that the skin of the aircraft does not change the radiating pattern and reflect it upwardly, as is the usual situation with antennas of this type utilizing a ground plane and high current loading at the base.

FIG. 4 illustrates a modified embodiment of the invention and like components are indicated by like numerals with suffix 0 added, The change in the structure is that the loading of a broadband antenna 58 can be from any conventional alternating current source. The antenna 58 is of a conventional 2 to 1 ratio to give broadband operation and eliminate tuning problems. The utilization of electrical chokes, indicated generally by numeral 60, surrounding the insulated broadband feed 59, achieves a zero current at the base, thus eliminating the necessity of a ground plane in the same manner as with the embodiment of FIG. I above. An epoxy filler or potting means 61 surrounds the chokes 60 to prevent the entrance of moisture and to hold the chokes, cable and radiator in place. The chokes provide a cheaper and more efl'icient way of achieving the loading at zero current to the base than the appropriate circuitry 15 shown in FIG. 1, cooperating with the antenna drive and receiver 24. The chokes can be made out of copper, for example, or any lossy material having a low q, or a q of 30 or below. Preferably, the chokes in total combination are made resonant at approximately one-fourth wavelength of the frequency band to thereby make the current approach zero at the base. These choke baluns are well known by those skilled in the art for use in impedance matching networks, and particularly with coaxial cables to minimize unbalance. The chokes, indicated generally by numeral 60, can be positioned within a housing 62 which is carried on an insulated base 64. The number of chokes 60 is dependent on the desired bandwidth. The housing 62 can be made from a very strong fiberglass and streamlined to an aerodynamic shape fore and aft, as best seen in FIG. 5. In this manner, it can be readily incorporated into an aircraft design and provide an extremely stable, high-strength antenna structure, and an antenna which is electrically insulated from the metallic skin of the aircraft, and which skin does not alter the radiated electromagnetic pattern.

Antennas of this type are designed to provide reliable operation in all directions for both transmission and reception of electromagnetic radiation, and will meet a service requirement ofa 1,000 hours of operation at air speeds up to 5 hundred miles per hour.

While in accordance with the Patent Statutes at least one best known form of the invention has been illustrated and described in detail, it is to be particularly understood that the invention is not to be limited thereto or thereby, but that the inventive scope is defined in the appended claims.

lclaim:

I. An antenna system, comprising:

an insulated mounting base;

a vertically directed radiator;

a vertically directed housing affixed at one end to the base and supporting the radiator at its opposite end by a nonconductive connection;

a coaxial cable extending through the housing and end feeding the radiator; and

means to electrically drive the radiator to produce a standing wave current thereon which current approaches zero at the mounting base and provides an omnidirectional vertically polarized electromagnetic wave pattern, the means including a plurality of chokes carried within the housing and concentrically aligned with one another and with the coaxial cable.

2. The antenna system according to claim 1 wherein the chokes are made of a lossy material having a q of not greater than 30, the chokes in combination being resonant at onefourth wavelength of a predetermined antenna frequency band.

3. The antenna system according to claim 1 wherein the housing has an insulating outer covering and an aerodynami cally streamlined configuration.

4. The antenna system according to claim 1 wherein potting means are provided within the housing to hold the chokes, cable, and radiator in fixed relation to each other. 

